Production of a porous aluminum filter for a diaphragm pump

ABSTRACT

A method produces a porous, arched aluminum fluidization element for a diaphragm pump for fluidizing, covering and delivering pulverized products, such as pulverized coal, using inert gas at pressures of up to 7 MPa. The fluidization element ensures that fluidizing gas is supplied and homogeneously distributed in the pump lower region, and the contour of the space for pulverized materials may be advantageously designed in the diaphragm deflection area and optionally adapted to the diaphragm guide rod. In this way, a homogeneous and reversible deformation of the diaphragm is obtained with minor wear as far as possible. At the end of the delivery process of the diaphragm pump, the diaphragm is applied to the arched, half-shell-shaped fluidization surface in an extensively flat manner, and a small dead volume can be obtained, which results in minimal space for pulverized materials with a high delivery rate and little high-pressure gas loss.

The invention relates to a method for producing a gas-permeable body which is formed with aluminum, and to a gas-permeable aluminum body produced in accordance with said method.

A body produced in accordance with the method according to the invention can be advantageously used as a loosening surface in a diaphragm pump for the fluidizing and charging of products in dust form, such as for example coal dust, by means of inert gas at pressures of up to 7 MPa as a filter element.

Continuous and inexpensive dense-stream conveying in the case of fluctuating dust quality of dusts for combustion for carbon and biomass gasification plants is of increasing importance in order, for example, to operate gasification plants economically and with high availability. This aim is achieved in a particular manner using a diaphragm pump as proposed in the patent application DE102016201182 of Jan. 27, 2016. The material for conveying in dust form is in this case drawn into the diaphragm pump from below, is charged and fluidized in a subsequent step, and is subsequently conveyed out under pressure. The residual gas volume in the dust chamber of the diaphragm pump is expanded in a final step after the material for conveying has been conveyed out, and the pump cycle begins again. Owing to this cyclic (discontinuous) mode of operation, it is normally the case that multiple pump heads are connected together in order to ensure continuous operation. For this purpose, the individual pump cycles are implemented with a phase offset with respect to one another. Filter materials which satisfy the requirements with regard to compressive strength and temperature resistance are for example the metallic filtration fabrics described in DE102012216084, sintered metal and sintered plastic. The described robust materials are available only in a flat or plate-like structure and not in the required size or dimensions. Mechanical processing into other geometrical shapes, such as for example half-shells, is not possible owing to the required filter fineness and the damage to or clogging of the porous filter structure that arises during mechanical processing.

From the special print from “Industriepumpen +Kompressoren” [“Industrial pumps and compressors”], 16th volume, book 3-2010, pages 120-123, Vulkan-Verlag Essen, with the title “Prozesspumpen mit zustandsüberwachter redundanter Schlauchmembran-Einspannung” [“Process pumps with state-monitored redundant hose diaphragm clamping”] by Heinz M. Nägel, a process pump is known, the double diaphragm of which is monitored with regard to integrity by means of coupling fluid and connection to a diaphragm rupture indicator.

The invention is based on the object of providing a filter element for feeding fluidizing and charging gas into the pressure vessel of a diaphragm pump, which filter element combines the requirements of pressure resistance, temperature resistance, adequate filter fineness, producibility with low outlay, and interaction with the diaphragm for the purposes of high diaphragm availability.

The object is achieved by means of a method for producing a gas-permeable aluminum body having the features of claim 1, and by means of a gas-permeable aluminum body produced in accordance with said method, having the features of claim 3.

The invention utilizes the realization that, for the mode of operation of the diaphragm pump, a uniformly distributed feed of the fluidizing gas in the lower region of the dust pump is essential. In the case of the loosening element produced in accordance with the invention, it is ensured that, by means of processing to form a domed filter element with a 3-dimensional shaping, any clogging of the material is avoided, and a uniform porosity can be realized.

The loosening element produced in accordance with the invention has a constant porosity, whereby it can be ensured that superfine dust particles do not ingress into the loosening surface during the expansion process of the dust chamber, giving rise to a uniformly distributed feed of fluidizing gas into the dust chamber during the charging process.

The invention permits a structural design of the dust chamber with a contour which is adapted in a particularly advantageous manner to the deflection of the diaphragm and possibly to the guide rod of the diaphragm. In this way, a uniform and reversible deformation of the diaphragm with the least possible wear is achieved.

After the completion of the conveying-out process of the diaphragm pump, it can be achieved that the diaphragm (3) lies substantially areally against the half-shell-shaped loosening surface (5). By means of this advantageous embodiment, a small dead volume can be achieved, which leads to a minimal dust chamber volume (10) with a simultaneously high conveying rate and low losses of high-pressure gas.

In the case of a hydraulically driven diaphragm pump for the pneumatic high-pressure conveyance of fluidized dusts, which diaphragm pump is equipped with the filter element produced in accordance with the invention, the pressure vessel that encloses the dust chamber has small dimensions with a minimized wall thickness, which leads to a reduction in production outlay.

In one particular embodiment of the invention, the loosening surface 5 has, at the lowest point, a circular opening to which there is fastened a dust pipe 7 through which the material for conveying in dust form can be conveyed in and conveyed out, which material for conveying thus cannot pass into the gas chamber 13.

Advantageous refinements of the invention are specified in the subclaims.

The invention will be discussed in more detail below in an exemplary embodiment, to an extent required for the purposes of understanding, on the basis of FIG. 1.

The diaphragm pump illustrated in FIG. 1 is an apparatus composed of two pressure-resistant half-shells (1, 12) which are connected to one another in gas-tight fashion by means of a flange connection (2). The flange connection has, aside from the possibility of easy disassembly of the dust pump, the additional function of fastening and clamping the diaphragm (3) and the loosening surface (5) by means of a filter flange (4). By means of the spherical geometry, it is thus possible for an advantageous deflection, which conserves the filter material, of the diaphragm into the dust chamber in the form of a paraboloid of revolution to be realized. The deflection of the diaphragm is in this case caused by an action of force of the hydraulic liquid, as described for example in DE102016201182. Abrupt changes are avoided, and after the completion of the conveying-out process, it can be achieved that the diaphragm (3) lies substantially areally against the half-shell-shaped loosening surface (5). By means of this advantageous embodiment, a small dead volume can be achieved, which leads to a minimal dust chamber volume (10) with a simultaneously high conveying rate and low losses of high-pressure gas. To avoid undesired movements and folding during the conveying-out process, the diaphragm is guided and stabilized in terms of its movement by means of a guide rod (9). The guide rod may, in a particularly advantageous embodiment, perform additional tasks such as for example the determination of the position of the diaphragm by means of measuring position transducers.

The invention is furthermore based on the problem of generating dense-stream conveying, described in DE 2005047583, by generating a fluidized bed within the dust chamber. This is achieved during the charging and conveying-out process by means of a homogeneous feed of gas via a half-shell-shaped and gas-permeable loosening surface (5). As filter material for the loosening surface (5), use is made of porous metal, for example aluminum, with an adequately small pore size and filter fineness of <20 μm. It can thus be ensured that superfine dust particles do not ingress into the loosening surface during the expansion process.

For the production of porous metal, liquid metal, for example aluminum, together with granulated salt is cast into a half-shell mold. Salt has a significantly higher melting point for example in relation to metals such as aluminum, and does not change into the liquid state of aggregation, but rather distributes uniformly in the melt. After solidification of the metal, the salt is washed out by means of a salt-dissolving liquid, and porous and gas-permeable metal is formed. An advantage of this method consists in the possibility of performing mechanical processing prior to the washing-out of the salt crystals. In this way, clogging of the pores is ruled out. The required porosity and filter fineness is set by means of the size of the salt grains.

In order to realize an advantageous flange seal (2), the loosening surface (5) may be formed in two layers; as a porous metal in the lower region and as a solid material in the flange region.

In a particular embodiment of the invention, the half-shell-shaped casting mold of the loosening surface (5) is expanded to include additional ring-shaped and/or punctiform support elements (8). It is thus possible for the half-shell-shaped loosening surface (5) composed of porous metal to be fitted and fastened into the lower pressure-resistant half-shell (12) composed of solid material. A gas chamber 13 is advantageously formed between the loosening surface composed of porous metal and the pressure-resistant half-shell, which gas chamber can be used for the distribution of the loosening and charging gas. The feed and discharge of the loosening and charging gas is realized by openings 6 in the lower pressure-resistant half-shell 12.

In the case of a hydraulically driven diaphragm pump for pneumatic high-pressure conveying of fluidized dusts, the reliable sealing of the dust chamber from the hydraulic chamber, which are separated by means of the diaphragm, is of particular importance. The deflection of the diaphragm and the associated drawing-in and conveying-out of the material for conveying in dust form is achieved by virtue of the hydraulic fluid in the hydraulic chamber situated above the diaphragm being forced in and forced out. Within this conveying process, the ingress of dust into the hydraulic liquid or of hydraulic liquid into the dust chamber is associated with considerable plant malfunctions and would lead to cumbersome repairs.

One special feature of the invention consists in the monitoring and assurance of the diaphragm leak-tightness. For this purpose, the diaphragm (3) is designed as a double diaphragm with integrated pressure sensor for leakage monitoring. In this way, it is possible for a hermetically sealed separation between hydraulic chamber (11) and dust chamber (10) to be ensured, and damage to the diaphragm can be identified in good time. Cumbersome repair and cleaning measures of the entire dust system or hydraulics system in the event of diaphragm damage are avoided, and the leak-tightness of the diaphragm is maintained during the fault situation.

In the case of the diaphragm 3 being designed as a double diaphragm, two resiliently elastic diaphragms are arranged so as to be mechanically supported relative to one another such that a closed intermediate space is formed between the diaphragms, which intermediate space can be monitored by means of a pressure sensor Δp (14). During fault-free operation, the intermediate space has a pressure lower than the pressure in the hydraulics chamber or the dust chamber. If a pressure increase is now detected in the intermediate chamber, a leakage of one of the two diaphragms of the double diaphragm is inferred. The two diaphragms may be arranged so as to be mechanically supported relative to one another in punctiform fashion by virtue of a layer of balls being arranged between them. The two diaphragms may be arranged so as to be mechanically supported relative to one another by virtue of a coupling liquid being introduced between them, which coupling liquid is operatively connected to the pressure sensor Δp.

The resiliently elastic diaphragm may be formed with an elastomer or a solid PTFE mixture. In the case of the double diaphragm, one of the two diaphragms may be realized by means of an elastomer, and the other of the two diaphragms may be realized by means of a solid PTFE mixture.

The invention is also provided by means of a diaphragm pump for fluidizing and conveying dusts, in the case of which

-   -   the pressure-resistant housing of the dust pump is composed of         two half-shells which are connected by means of a flange         connection and into which a diaphragm and a loosening surface         are flange-mounted,     -   the loosening surface is formed in layers from porous material         in the lower region and solid material in the region of the         flange connection,     -   the loosening surface is designed as a half-shell and comprises         support elements, and a gas chamber exists between         pressure-resistant lower half-shell and loosening surface.

The present invention has been discussed in detail for illustrative purposes on the basis of specific exemplary embodiments. Here, elements of the individual exemplary embodiments may also be combined with one another. The invention is therefore intended not to be restricted to individual exemplary embodiments, but rather restricted only by the appended claims.

LIST OF REFERENCE DESIGNATIONS

-   1 Pressure-resistant upper half-shell, hydraulics half-shell -   2 Container flange -   3 Diaphragm -   4 Filter flange -   5 Loosening surface composed of porous metallic filter material -   6 Openings for charging and conveying gas, gas pipe -   7 Inner pipe for inlet and outlet of the dust, dust pipe -   8 Ring-shaped, punctiform, strip-shaped support elements -   9 Diaphragm guide/guide rod -   10 Dust chamber -   11 Hydraulics chamber -   12 Pressure-resistant lower half-shell, dust half-shell -   13 Gas chamber -   14 Pressure sensor Δp 

1. A method for producing a gas-permeable body which is formed with aluminum, in which method salt is admixed to an aluminum melt, the mixture composed of aluminum melt and salt is allowed to solidify, the solidified mixture is processed into the desired body form, and the salt is removed from the body form by means of a dissolution process.
 2. The method for producing a gas-permeable body as claimed in claim 1, wherein the desired porosity and filter fineness is set by means of the size of the salt grains.
 3. A gas-permeable body composed of aluminum, which is produced by means of the following sequence of working steps: admixing salt to an aluminum melt, solidifying the mixture composed of aluminum melt and salt, processing the solidified mixture into the desired body form, and removing the salt from the body form by means of a dissolution process.
 4. The gas-permeable body as claimed in claim 3, wherein a porous metallic filter material is formed.
 5. The gas-permeable body as claimed in claim 4, wherein the fineness of the filter material amounts to <40 μm.
 6. The gas-permeable body as claimed in claim 4, wherein the fineness of the filter material amounts to <20 μm.
 7. The gas-permeable body as claimed in claim 3, wherein the gas-permeable body is connected to a gas-impermeable body so as to form a unit.
 8. The gas-permeable body as claimed in claim 3, wherein the gas-permeable body is part of a gas-impermeable aluminum body.
 9. The gas-permeable body as claimed in claim 3, wherein the body form is adapted to the deflected form of a diaphragm of a dust pump.
 10. The gas-permeable body as claimed in claim 3, wherein a dust feed pipe (7) is connected at the lowest point.
 11. The gas-permeable body as claimed in claim 3, wherein at least one support (8) is formed integrally. 